AGE-DEPENDENCE OF PHOTOSYNTHETIC ACTIVITY, CHLOROPHYLL FLUORESCENCE PARAMETERS AND CHLOROPLAST ULTRASTRUCTURE IN AUREA AND GREEN FORMS OF NICOTIANA-TABACUM SU SU MUTANT/

The age dependence of the photosynthetic performance, chlorophyll fluo rescence and chloroplast ultrastructure of green form and Chi b-defici ent form (aurea) of tobacco Su/su mutant were compared The most pronou nced differences between the aurea and green tobacco found in young le aves diminished with leaf age. Slower accumulation of the photosynthet ic pigments during the development of aurea leaves was accompanied by a slower accumulation of LHC antennae of both photosystems, particular ly that of PS2, and by retention of an increase in the capacity of PS2 photochemistry, measured as F-V/F-M. The ratio F-V/F-M, however, incr eased rapidly during maturation of aurea leaves, and finally the matur e aurea leaves exhibited higher values of this ratio than the green on es. Rates of photosynthesis at saturating irradiance (P-max) and satur ating CO2 concentration (P-sat) decreased with leaf age for both aurea and green tobacco, being always higher in aurea leaves than in leaves of green tobacco of comparable age. All these characteristics indicat ed retarded development of aurea leaves. Also the chloroplast ultrastr ucture, particularly grana formation, exhibited slower development. Th e decrease in P-max and P-sat with leaf age in both tobacco forms and retardation in the development of aurea leaves can explain higher valu e of P-max usually found in aurea tobacco.